You are supposing it was an intentional technique, but chances are it was an editorial fix.
It was an intentional technique:
In ET they first made a wide shot of Nimoy and his lyra facing
the fountain-planter and the tanning lady on the (oddly elevated!) sitting bench.
Next they made Nimoy get up and change position and made a close-up shot of him with the fountain and the sitting bench at his back.
In the editing room the footage was combined to create the illusion of two
circular rooms separated only by the food synthesizer and intercom corridor.
The same technique was applied in CL.